1. Field of the Invention
This invention relates generally to semiconductor body holders and more particularly to semiconductor body holders useful in the practice of temperature gradient zone melting.
2. Description of the Prior Art
In the manufacture of a semiconductor device, it is often necessary to alter or tailor the conductivity type of a body of semiconductor material. This alteration is achieved by distributing atoms of a conductivity modifying dopant in a selected region or selected regions of the body. Frequently, techniques employed to achieve that distribution require the heating of the semiconductor body.
Recently, it has been discovered that a preferred technique of altering the conductivity of the semiconductor body in a variety of applications is the technique of temperature gradient zone melting. Early teachings of temperature gradient zone melting are found in U.S. Pat. No. 2,813,048 issued to W. G. Pfann, and in a book by Pfann entitled Zone Melting (John Wiley & Sons, Inc., 1966). More recent applications of temperature gradient zone melting are disclosed and claimed in U.S. Pat. Nos. 3,899,361 and 3,899,362 to Thomas R. Anthony and Harvey E. Cline and assigned to the assignee of the present invention. The aforementioned U.S. patents to Anthony and Cline are incorporated herein by reference.
As taught in the aforementioned book by Pfann, temperature gradient zone melting involves the migration of a melt of a first material through a body of a second material under the influence of a temperature gradient maintained across the second material and finally a recrystallization of the melt after migration. In the application of temperature gradient zone melting to the production of semiconductor devices, the first material usually comprises a metal such as aluminum, tin-aluminum alloy or gold-antimony alloy while the second material comprises a semiconductor material such as silicon, germanium or the like.
Critical to the successful implementation of temperature gradient zone melting in the manufacture of semiconductor devices is the maintenance of a unidirectional temperature gradient across the semiconductor material. That is, for any desired direction of migration of the conductivity altering dopant through a body or wafer of semiconductor material, a temperature gradient across the body of semiconductor material must be established in exactly the same direction. Presently, in the production of semiconductor devices by temperature gradient zone melting, this preferred direction of migration and thus of the required temperature gradient is normal to the major surfaces of the body or wafer. The existence of temperature gradients in any other directions (lateral or oblique to the major surfaces of the wafer) will cause the migration of the conductivity altering material in these other directions thereby causing the resulting doped zone to be irregular or misdirected and thus adversely affecting the performance of the device.
It has been discovered that the intensity and orientation of the desired temperature gradient can be enhanced by the provision of a heat sink or cooling block on a side of the semiconductor body opposite that which is heated. Due to the possible bowing of the semiconductor body during heating, it is undesirable to place the semiconductor body in contact with the heat sink during the temperature gradient zone melting. Such a bowing would cause only partial contact between the semiconductor body and the heat sink thereby giving rise to undesirable lateral or transverse temperature gradients.
In his copending U.S. patent application Ser. No. 578,736, filed May 19, 1975 and entitled "Heating Apparatus For Temperature Gradient Zone Melting", incorporated herein by reference, John Boah discloses and claims various constructions for semiconductor body supports or holders which in cooperation with the weight of the body, support the body a slight distance above a heat sink thereby avoiding contact between the semiconductor body and the heat sink while eliminating any lateral temperature gradients stemming from that contact. However, such supports which rely on the weight of the semiconductor body for the support of the body are useful only in apparatus where the body is heated from above and where the heat sink is disposed below the body. As the art of temperature gradient zone melting progresses, the heating of the bodies from various other locations relative to the body will be required. Morever, modern techniques of temperature gradient zone melting require that the semiconductor body being treated undergo certain movement while being heated to insure the uniformity of orientation and intensity of the temperature gradient. Such a teaching is found in U.S. patent application Ser. No. 645,675, filed Dec. 31, 1975, in the names of Thomas R. Anthony and Harvey E. Cline and assigned to the assignee of the present invention. This application is incorporated herein by reference. With such a movement of the semiconductor bodies while being treated, the bodies may slide off the supports upon which they rest, damaging the body and causing the misdirection of the desired temperature gradient.
However, it must be appreciated that not all means of positively holding a semiconductor body during processing by temperature gradient zone melting will be suitable. During the heating of the body, the body will radiatively emit heat to the heat sink thereby maintaining the temperature gradient across the body. Any support or holder disposed between the semiconductor body and the heat sink will necessarily block or shadow some of this radiation causing the formation of undesirable lateral or transverse temperature gradients. Furthermore, conduction of heat from the semiconductor body to the holder or support through the contacting surfaces of these two members will cause the formation of cool spots on the semiconductor body thereby distrubing the desired temperature gradient.
It is therefore an object of the present invention to provide a new and improved semiconductor body holder which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide a semiconductor body holder which allows a semiconductor body to be supported in any orientation relative to a source of heat for heating the body.
It is another object of the present invention to provide a semiconductor body holder which adequately supports a semiconductor body while the body is being moved during processing.
It is another object of the present invention to provide a semiconductor body holder which minimizes the blocking of radiation emitted by the semiconductor body to a heat sink.
It is another object of the present invention to provide a semiconductor body holder which minimizes the conduction of heat away from the semiconductor body through the holder.